Method and control unit for operating a valve

ABSTRACT

A method for operating a valve, in particular a fuel injector of an internal combustion engine of a motor vehicle, in which an auxiliary variable is obtained as a function of at least one electrical operating variable of an electromagnetic actuator driving a component of the valve, in particular a valve needle, and in which the auxiliary variable is checked for the presence of a predefinable characteristic. A reference variable which characterizes the operating behavior of the electromagnetic actuator is ascertained, the auxiliary variable is modified as a function of the reference variable to obtain a modified auxiliary variable, and the modified auxiliary variable is checked for the presence of the predefinable characteristic.

FIELD OF THE INVENTION

The present invention relates to a method for operating a valve, inparticular a fuel injector of an internal combustion engine of a motorvehicle, in which an auxiliary variable is obtained as a function of atleast one electrical operating variable of an electromagnetic actuatordriving a component of the valve, in particular a valve needle, and inwhich the auxiliary variable is checked for the presence of apredefinable characteristic. The present invention also relates to acontrol unit for operating a valve of this type.

BACKGROUND INFORMATION

Methods and devices of the aforementioned type are usually used toobtain information about an operating state of the valve. Particularlyimportant changes in the operating state, for example a transition froman open state to a closed state, are derivable from extremes of a timecharacteristic of the auxiliary variable, at least in some operatingmodes or operating points of conventional injectors.

However, the evaluation accuracy of conventional methods is ofteninsufficient, in particular in the event of short activation timesand/or minimal valve lifts.

SUMMARY

An object of the present invention is to improve a method and a controlunit of the type mentioned above in such a way that a more preciseevaluation and the obtaining of information on an operating state arepossible even in the event of minimal valve lifts.

In accordance with the present invention, this object may be achievedusing an example method that ascertains a reference variable whichcharacterizes the operating behavior of the electromagnetic actuator,modifies the auxiliary variable as a function of the reference variableto obtain a modified auxiliary variable, and checks the modifiedauxiliary variable for the presence of the predefinable characteristic.

Preparing the auxiliary variable in this way according to the presentinvention allows for a particularly precise evaluation, thus providinghigh evaluation accuracy with regard to detecting changes in theoperating state of the valve, in particular in the event of shortactivation times or minimal valve lifts.

According to one variant of the present invention, a time characteristicof an actuator voltage or an actuator current is particularlyadvantageously used as the at least one electrical operating variablefor forming the auxiliary variable, i.e., a time characteristic of anelectrical voltage applied to a solenoid coil of an electromagneticactuator or a time characteristic of the current flowing through thesolenoid coil.

According to the present invention, it has been found that a firstsignal portion of the auxiliary variable, which is generated on thebasis of the magnetic and electrical properties of the magnetic circuitof the electromagnetic actuator, and a second signal portion which isgenerated by a movement of elements of the magnetic circuit and thus bythe change in geometric parameters of the magnetic circuit, are alwayspresent regardless of the specific formation of the auxiliary variable(e.g., via the actuator voltage and/or the actuator current).

In operating areas of this type, in which the solenoid armature, as themoving component of the magnetic circuit, moves only a relatively shortdistance (actual lift much smaller than maximum nominal lift) orquickly, the portion of the signal of the auxiliary variable generatedby the armature movement decreases, while the first signal portion ofthe auxiliary variable, which is generated on the basis of the magneticand electrical properties of the magnetic circuit of the electromagneticactuator, remains generally the same.

This makes it more difficult to detect a predefinable characteristic inthe auxiliary variable using conventional methods.

Using the reference variable according to the present invention, whichpreferably simulates the first signal portion of the auxiliary variable,this portion being generated on the basis of the magnetic and electricalproperties of the magnetic circuit of the electromagnetic actuator, theparticularly interesting second signal portion, which is generated by amovement of elements of the magnetic circuit and thus by a change ingeometric parameters of the magnetic circuit, may thus be advantageouslyselectively evaluated.

According to another advantageous variant of the present invention, aparticularly efficient evaluation results if the reference variable isobtained with the aid of a model which simulates a dynamic behavior ofthe electromagnetic actuator, in particular its magnetic circuit.

According to another variant of the present invention, it may beparticularly advantageously provided that the model simulates a timecharacteristic of the at least one electrical operating variable and/orthe auxiliary variable, in particular the provision thereof without amovement of a movable component (e.g., a solenoid armature) of theelectromagnetic actuator.

Alternatively or additionally, the reference variable may be obtained asa function of the at least one electrical operating variable, inparticular preferably from values of the at least one electricaloperating variable obtained in an operating mode of the electromagneticactuator in which there is no movement of a movable component (e.g.,solenoid armature) of the electromagnetic actuator. For this purpose,the values of the at least one electrical operating variable arepreferably detected by measurement during a particular activation of theelectromagnetic actuator. The particular activation, characterized forexample by a relatively short activation time, advantageously ensuresthat an armature movement does not already occur despite the activation.

Another very advantageous variant of the present invention provides thatthe modified auxiliary variable is obtained in that the referencevariable is subtracted from the auxiliary variable, which imposesparticularly minimal requirements on a control unit which carries outthe example method according to the present invention or on a processorincluded therein.

According to another advantageous variant of the present invention, itis furthermore possible to divide a difference between the auxiliaryvariable and the reference variable by the auxiliary variable and/or thereference variable to obtain the modified auxiliary variable.

According to another very advantageous variant of the present invention,the reference variable according to the present invention may be storedafter it is ascertained, so that it is available for carrying out theexample method according to the present invention in the future and doesnot have to be constantly re-ascertained.

It may be of particular interest to implement the operating methodaccording to the present invention in the form of a computer programwhich may be stored on an electronic and/or optical storage medium andwhich is executable by a control and/or regulating system, e.g., for aninternal combustion engine.

Additional advantages, features and details arise from the descriptionbelow, in which different exemplary embodiments of the present inventionare illustrated with reference to the figures. The features mentioned inthe description may each be used for the present invention eitherindividually or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of an internal combustion enginehaving multiple injectors operated in accordance with the presentinvention.

FIGS. 2 a through 2 c show schematic representations of a detailed viewof an injector from FIG. 1 in three different operating states.

FIG. 3 shows a simplified flow chart of a specific embodiment of themethod according to the present invention.

FIG. 4 shows a schematic representation of a time characteristic of anactivating current for a valve operated in accordance with the presentinvention.

FIG. 5 shows a time characteristic of an auxiliary variable obtainedfrom an electrical operating variable of the valve from FIG. 2 a as wellas variables derived therefrom in accordance with the present invention.

FIG. 6 shows a function diagram for implementing a variant of the methodaccording to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In FIG. 1, an internal combustion engine is identified as a whole byreference numeral 10. It includes a tank 12 from which a delivery system14 delivers fuel to a common rail 16. Multiple electromagneticallyactuated injectors 18 a through 18 d, which inject the fuel directlyinto combustion chambers 20 a through 20 d assigned to them, areconnected thereto. The operation of internal combustion engine 10 iscontrolled or regulated by a control and regulating system 22, whichactivates injectors 18 a through 18 d, among other things.

FIGS. 2 a through 2 c show schematic representations of injector 18 aaccording to FIG. 1 in a total of three different operating states. Theother injectors 18 b, 18 c, 18 d, which are also illustrated in FIG. 1,have a corresponding structure and functionality.

Injector 18 a has an electromagnetic actuator which includes a solenoidcoil 26 and a solenoid armature 30 which cooperates with solenoid coil26. Solenoid armature 30 is connected to a valve needle 28 of injector18 a in such a way that it is movable relative to valve needle 28 in anon-vanishing mechanical clearance in relation to a vertical directionof movement of valve needle 28 in FIG. 2 a.

This results in a two-part mass system 28, 30, which drives valve needle28 with the aid of electromagnetic actuator 26, 30. This two-partconfiguration improves the mountability of injector 18 a and reducesundesirable rebounding of valve needle 28 when it strikes its valve seat38.

In the present configuration illustrated in FIG. 2 a, the axialclearance of solenoid armature 30 on valve needle 28 is limited by twostops 32 and 34. However, at least lower stop 34 in FIG. 2 a could beimplemented in the form of an area of the housing of injector 18 a.

As shown in FIG. 2 a, a corresponding elastic force against valve seat38 is applied to valve needle 28 in the area of housing 40 by a valvespring 36. In FIG. 2 a, injector 18 a is shown in its open state. Inthis open state, solenoid armature 30 is moved upward by an energizationof solenoid coil 26 in FIG. 2 a, so that it moves valve needle 28 out ofits valve seat 38 against the elastic force by engaging with stop 32.This enables fuel 42 to be injected into combustion chamber 20 a(FIG. 1) by injector 18 a.

As soon as the energization of solenoid coil 26 by control unit 22(FIG. 1) is ended, valve needle 28 moves toward its valve seat 38 underthe effect of the elastic force applied by valve spring 36 and carriessolenoid armature 30 along with it. A transmission of force from valveneedle 28 to solenoid armature 30 again takes place with the aid ofupper stop 32.

As soon as valve needle 28 ends its closing movement by striking valveseat 38, solenoid armature 30 may continue to move downward, as shown inFIG. 2 b, due to the axial clearance in FIG. 2 b, until it rests againstsecond stop 34, as illustrated in FIG. 2 c.

According to the present invention, the method described below withreference to the flow chart according to FIG. 3 is carried out to obtainparticularly precise information about an operating state or a change inthe operating state of injector 18 a.

In a first step 100 of the method according to the present invention, anelectrical operating variable of electromagnetic actuator 26, 30 (FIG. 2a), for example the actuator voltage in the present case, which isapplied to solenoid coil 26 of the actuator, is detected. This may takeplace with the aid of a measuring instrument integrated into controlunit 22 (FIG. 1) in a conventional manner. An auxiliary variable m (FIG.5) is then formed as a function of actuator voltage u, also in step 100.

In the simplest case, auxiliary variable m may be identical to theactuator voltage. However, auxiliary variable m may also be generallyobtained as a function of the actuator voltage and/or the actuatorcurrent flowing through solenoid coil 26. A filtering as well as othercommon signal processing methods may also be used to obtain auxiliaryvariable m from the actuator voltage and/or the actuator current.

A reference variable mref (FIG. 5), which characterizes the operatingbehavior of electromagnetic actuator 26, 30, is ascertained in asubsequent step 110.

According to a preferred specific embodiment of the present invention,reference variable mref is obtained with the aid of a model 200 (FIG. 6)which simulates a dynamic behavior of electromagnetic actuator 26, 30,in particular its magnetic circuit. For this purpose, it may beparticularly advantageously provided that model 200 simulates a timecharacteristic of the at least one electric operating variable (actuatorvoltage, actuator current) and/or auxiliary variable m, which isobtained, in particular, without a movement of a movablecomponent—solenoid armature 30 in the present case—of theelectromagnetic actuator.

In step 120 of the method according to the present invention, auxiliaryvariable m is subsequently modified as a function of reference variablemref to obtain a modified auxiliary variable mmod (FIG. 5).

According to studies by the applicant, auxiliary variable mmod, which ismodified in the manner described above, has a particularly strongcorrelation with important changes in the operating state of valve 18 aand is therefore ideally suited to detecting such changes in theoperating state.

In particular, it is possible, by forming the modified auxiliaryvariable, to extremely precisely ascertain a hydraulic closing point intime of valve 18 a at which valve needle 28 reaches its closed positionin the area of the injection holes or of valve seat 38.

FIG. 4 shows a schematic representation of an exemplary timecharacteristic of an activating current I for electromagnetic actuator26, 30 (FIG. 2 a) of valve 18 a during an activation for a fuelinjection.

To enable valve 18 a to open rapidly from its closed state at t=t0,activating current I is increased from point in t0, which corresponds tothe activation start, from value I=0 to booster current Iboost. Boostercurrent Iboost is reached at point in time t1. The booster current ismaintained until subsequent point in time t2.

It may be assumed that valve 18 a has reached its open state at end t2of the so-called booster phase, which lies between point in time t0 andpoint in time t2. To continue to keep the valve open at points in timet≧t2, activating current I is now reduced not to zero but to so-calledholding current Ih.

According to FIG. 4, holding current Ih is maintained until point intime t3. Time difference t3−t0 defines total electrical activating timeET of valve 18 a or its electromagnetic actuator 26, 30.

At the end of activating time ET, i.e., starting at t=t3, control unit22 no longer applies an activating current or a corresponding activatingvoltage to electromagnetic actuator 26, 30, so that the activatingcurrent still present finally decreases to zero by point in time t4,according to the laws of induction.

FIG. 5 shows a time characteristic of needle lift h of valve needle 28(FIG. 2 a), which results during an activation according to activatingcurrent characteristic I described above (cf. FIG. 4) at very shortelectrical activation times ET.

In activation operations of this type, in which a relatively shortactivation time ET or a relatively small maximum valve lift h ispresent, auxiliary variable m usually does not have any characteristicswhich may be very easily and directly evaluated to reliably determineactual hydraulic closing point in time ts (FIG. 5). At actual closingpoint in time ts, auxiliary variable m examined according to the presentinvention has a non-vanishing curvature in the present case, but not alocal extreme which is easily detectable, for example.

The representation of the variables shown in FIG. 5 is not true toscale. In particular, auxiliary variable m may indeed have a far lesssignificant characteristic at point in time ts than is shown in thepresent illustration in FIG. 5.

Using the principle according to the present invention, a referencevariable mref is therefore formed to permit an efficient evaluation ofauxiliary variable m.

A modification of auxiliary variable m according to the presentinvention with the aid of reference variable mref results in modifiedauxiliary variable mmod, which has a pronounced local minimum Min atclosing point in time ts, as shown in FIG. 5.

Accordingly, the formation of reference variable mref according to thepresent invention and the subsequent modification of auxiliary variablem as a function of reference variable mref, whereby a modified auxiliaryvariably mmod is obtained, advantageously permit a simple evaluation ofauxiliary variable m or modified auxiliary variable mmod for thepresence of a change in the operating state, such as the closingoperation of valve 18 a described above.

The principle according to the present invention has proven to beparticularly reliable, in particular at relatively short activationtimes ET as well as relatively small maximum needle lifts h.

The variables described above—auxiliary variable m, reference variablemref, modified auxiliary variable mmod—are preferably a correspondingtime characteristic of the relevant variables. In one embodiment of theoperating method according to the present invention, a sufficiently highsampling rate for the respective variables m, mref, mmod must beselected according to the desired precision, with the aid of digitalsignal processing.

A formation of modified auxiliary variable mmod which requiresparticularly little computing complexity, is achieved in that referencevariable mref is subtracted from auxiliary variable m.

According to the present invention, it may furthermore be provided thata difference is obtained from variables m, mref, which, in turn, isdivided by auxiliary variable m and/or reference variable mref to obtainmodified auxiliary variable mmod, for example:

mmod=(m−mref)/m.

FIG. 6 shows a block diagram of an arithmetic structure by way ofexample for ascertaining modified auxiliary variable mmod according tothe present invention. Reference variable mref is formed from actuatorvoltage u with the aid of model 200 according to the present invention.

Auxiliary variable m is obtained with the aid of function block 201—alsoas a function of actuator voltage u in the present case.

In the simplest case, auxiliary variable m may be identical to actuatorvoltage u, as described previously. In this case, function block 201 maybe dispensed with. However, auxiliary variable m may also be generallyobtained as a function of actuator voltage u and/or actuator current Iflowing through solenoid coil 26. A filtering as well as other commonsignal processing methods may also be used to obtain auxiliary variablem from the actuator voltage and/or the actuator current.

Reference variable mref and auxiliary variable m itself are thensupplied to subtracter 202, which ascertains difference m−mreftherefrom. Due to the properties of reference variable mref according tothe present invention, difference m−mref obtained at the output offunction block 202 essentially reflects a signal portion of auxiliaryvariable m which is obtained on the basis of the armature movement ofsolenoid armature 30 (FIG. 2 a).

In a preferred specific embodiment of the present invention, thisdifference may therefore be used directly as a modified auxiliaryvariable mmod to be checked for an interesting characteristic, e.g., alocal minimum Min (FIG. 5).

In another preferred specific embodiment of the present invention,instead of model 200 (FIG. 6), reference variable mref is obtaineddirectly as a function of at least one electrical operating variable,e.g., actuator voltage u or actuator current I, from such values ofthis/these variable(s) u, I which result in an operating mode ofelectromagnetic actuator 26, 30 in which there is no movement of themovable component, i.e., solenoid armature 30 of electromagneticactuator 26, 30 in the present case.

For this purpose, electromagnetic actuator 26, 30 may be selectivelyactivated, for example, in such a way that an actuator movement does notalready result. This is achieved, for example, by a sufficiently shortactivation time ET. During the activation, the values of the at leastone electrical operating variable u, I are detected by measurement to beused henceforth as reference variable mref in the sense of the methodaccording to the present invention.

Reference variable mref ascertained according to the present inventionmay also be particularly advantageously stored after its ascertainment110 (FIG. 3) for a future use so that it does not have to be constantlyre-ascertained.

Although the method according to the present invention is preferablyused to detect characteristics Min which are not ascertainable usingconventional methods, other more easily detectable changes in operatingstates may also generally be ascertained using the method according tothe present invention, which results in a standard evaluation andcorrespondingly little complexity.

It is also possible to use the method according to the present inventionalternately with other detection methods for detecting othercharacteristics of auxiliary variable m.

The principle according to the present invention may be used regardlessof whether auxiliary variable m, which has interesting characteristicMin, is obtained with the aid of analog or digital signal processing orby carrying out conventional signal processing or preparation processes,such as filtering, differentiation or integration. In such cases, it isonly necessary to ensure that model 200 simulates processing steps whichcorrespond to the signal processing processes used, so that referencevariable mref obtained on the basis of the model matches auxiliaryvariable m to be evaluated.

The same applies to variants of the present invention in which referencevariable mref is ascertained from variables u, I obtained by measurementinstead of a model-based ascertainment of reference variable mref.

In the variants of the present invention in which reference variablemref is ascertained from variables u, I obtained by measurement, it maybe furthermore particularly important for the actuator or valve 18 a tohave a securely closed state during activation of actuator 26, 30 forascertaining corresponding measured values of variables u, I to formreference variable mref, so as to avoid obtaining signal portionsgenerated by the armature movement as components of reference variablemref.

1-14. (canceled)
 15. A method for operating a valve, comprising:obtaining an auxiliary variable as a function of at least one electricaloperating variable of an electromagnetic actuator driving a valve needleof the valve; ascertaining a reference variable which characterizes anoperating behavior of the electromagnetic actuator; modifying theauxiliary variable as a function of the reference variable to obtain amodified auxiliary variable; and checking the modified auxiliaryvariable for presence of a predefinable characteristic.
 16. The methodas recited in claim 15, wherein the valve is a fuel injector of aninternal combustion engine.
 17. The method as recited in claim 15,wherein a time characteristic of one of an actuator voltage or anactuator current is used as at least one electrical operating variablefor forming the auxiliary variable.
 18. The method as recited in claim15, wherein the reference variable is obtained with the aid of a modelwhich simulates a dynamic behavior of the electromagnetic actuator. 19.The method as recited in claim 18, wherein the model simulates a dynamicbehavior of a magnetic circuit of the electromagnetic actuator.
 20. Themethod as recited in claim 18, wherein the model simulates a timecharacteristic of at least one of: i) the at least one electricaloperating variable, and ii) the auxiliary variable, which resultswithout a movement of a movable component of the electromagneticactuator.
 21. The method as recited in claim 15, wherein the referencevariable is obtained as a function of the at least one electricaloperating variable.
 22. The method as recited in claim 21, wherein thereference variable is obtained from values of the at least oneelectrical operating variable, which result in an operating mode of theelectromagnetic actuator in which there is no movement of a movablecomponent of the electromagnetic actuator.
 23. The method as recited inclaim 22, wherein the values of the at least one electrical operatingvariable are detected by measurement during an activation of theelectromagnetic actuator.
 24. The method as recited in claim 15, whereinthe modified auxiliary variable is obtained in that the referencevariable is subtracted from the auxiliary variable.
 25. The method asrecited in claim 24, wherein a difference between the auxiliary variableand the reference variable is divided by at least one of the auxiliaryvariable and the reference variable, to obtain the modified auxiliaryvariable.
 26. The method as recited in claim 15, wherein the referencevariable is stored after it is ascertained.
 27. The method as recited inclaim 26, wherein the stored reference variable is used to modify theauxiliary variable.
 28. A storage medium storing a computer program foroperating a valve, the computer program, when executed by a processor,causing the processor to perform the steps of: obtaining an auxiliaryvariable as a function of at least one electrical operating variable ofan electromagnetic actuator driving a valve needle of a valve;ascertaining a reference variable which characterizes an operatingbehavior of the electromagnetic actuator; modifying the auxiliaryvariable as a function of the reference variable to obtain a modifiedauxiliary variable; and checking the modified auxiliary variable forpresence of a predefinable characteristic.
 29. The storage medium asrecited in claim 28, wherein the storage medium is one of an electronicstorage medium and an optical storage medium.
 30. A control orregulating system for operating a valve system, the system configured toobtain an auxiliary variable as a function of at least one electricaloperating variable of an electromagnetic actuator driving a valve needleof a valve, ascertain a reference variable which characterizes anoperating behavior of the electromagnetic actuator, modify the auxiliaryvariable as a function of the reference variable to obtain a modifiedauxiliary variable, and check the modified auxiliary variable forpresence of a predefinable characteristic.